Implementation of Multi-Subcarrier
Multiple Access by Digital Modulation
* CJK2016 in China * Keio University, Japan B3 Hiromu Kamei
Background 1
• Nowadays, many structures(e.g. tunnels and bridges) are getting old in Japan
• It became compulsory for local governments to inspect the safety of tunnels and bridges because the ceiling collapse accident happened at Sasago-tunnel
others 82%
old 18%
others
old 20%
others 66%
old 34%
others 57%
old 43%
2013 2023
ca.71,000 ca.171,000
ca.2,000 ca.3,000
The present state and the future estimation
of structures
The rate of 50 years passed bridges
The rate of 50 years passed tunnels
• Inspections do not seem to be carried out smoothly because of the lacks of funds and engineers
3
Cities Towns Villages
0% 20% 40% 60% 80% 100%
4%
32%
37%
67%
59%
63%
29%
9%
0 1~5 6~
※BPR investigation(2014.11)
※BPR investigation(2013.4)
Required supports by municipalities to the government
0% 20% 40% 60% 80% 100%
38% 58% 86%
24%28% 48% Technical advices
Holding lectures
Sending professionals Financial suppports
Maintenance a manual for a labor productivity unit Maintenance a manual for inspection
Background 2
The number of engineers for inspecting bridges The number of bridges and its administrators
Problem summary
• There are many old structures which should be inspected
• It runs short of engineers to inspect structures
• It costs a lot for inspections of structures
5
We use RFID, low power sensors and an energy harvesting technology to realize this system
Proposal
Faults detection system for structures by vibration tests with wireless and batteryless sensors
Technical problem
We need to get multiple sensors data continuously and simultaneously in vibration tests
Multi-Subcarrier Multiple Access
Multi-Subcarrier Multiple Access
Multi-Subcarrier Multiple Access(MSMA) enable to communicate
with multiple RF tags continuously and simultaneously. We also call MSMA as pseudo-FDMA. Tags communicate by using each
assigned subcarrier. On modulating a subcarrier to a carrier,
interference are generated. However, we can cancel them by digital signal processing.
7
Only it has been verified of transmitting data by analog modulation in MSMA
The purpose is to verify the feasibility of digital modulation in MSMA
Challenge
Implementation
The tag used for generating a subcarrier
The modulated subcarrier signal
1
0
0 1 0 0 1 1 1
Symbol period Subcarrier period
Interference by subcarrier generation in MSMA
9
SC5 SC4
SC3 SC2
SC1 SC6
Signal power
frequency
…
fc+fs
Interference of SC1 Interference of SC2
fc fc+2fs fc+3fs fc+4fs fc+5fs fc+6fs
fc : Carrier frequency
fs : Subcarrier frequency
Experimental structure
Splitter
MCU Signal generator
PC Tag
(LabVIEW)
Tag
USRP Splitter
Used instruments
• MSP430F5438
• USRP-2920
• LabVIEW 2015
MCU
Experiment -Frequency spectrums-
11 10KHz
30KHz
10KHz+30KHz 916.01MHz
916.03MHz
916.03MHz
916.01MHz
916.03MHz
Result 1
The received signal
The signal after
interferences rejection The received signal and the signal
after interferences rejection
Result 2
13
Demonstration
Conclusion
• Porting the program into USRP
• Experimentation in wireless
• Using a real sensor
• Proceeding batteryless part
15 Future work
Result
I could verify the feasibility of digital modulation in MSMA
